正常雨水偏酸性，pH约为5.6，这是因为大气中的 A气体溶于水的缘故．酸雨是指pH小于5.6的降水，主要是由人为排放的硫氧化物和氮氧化物等酸性气体转化而成的，发生的反应主要有：

①SO₂+H₂O═H₂SO₃      ②2H₂SO₃+O₂═2H₂SO₄

③2NO+O₂═2NO₂（快速）   ④3NO₂+H₂O═2HNO₃+NO

请回答下列有关问题：

（1）A气体的化学式为　____ 　．

（2）上述四个化学反应中的所有物质中，属于酸的有____种．

（3）由③、④两个反应可知，NO₂中的氮元素最终以　____ 　（写化学式）物质形式存在．

B

    I'm Tom and I like sports. Basketball is my favourite. I play it in. my school in the morning. My school is big and there is a playground and a sports hall in it. Every morning, many teachers and students play sports in the playground. I play there with my friends too. When the weather is bad we play in the sports hall. It's on the left of the playground. Now I'm in the sports hall but I don't play basketball. Some students from London are in our school and I'm their guide (导游).

    My family also like sports too. My parents kick(踢)jianzi near our home every morning. My sister Mary plays table tennis with her classmates in their school. It is small but beautiful.